Technically, if you ve implemented steel storm eating mana on hit/when hit its cool, but
in accordance with all other spells, it should eat mana only when hit/on hit.
not when cast at the start of combat due to pallida?
Other option would be making all spell gems cast automatically consume their mana cost. but i didnt say it, will be a gamechanger.
Also, if its consumes life instead of mana, you can do a suicide trigger team now? 
some trigger only spells have mana cost right
in fact quite high usually, notables are steel storm/mutilate/rend
afaik at least steel storm now quenches mana for good
and cerberus explicitely says that his spells cost 0 mana so it overrides that stuff anyway
more concerned about pallida in fact / in before combat situations.
or anyway can try to even build suicide trigger team on it though have to circumvent inability to cast health cost spells at low health or find another auto-suicide ways at low health 
basically its like programming but you dont get paid
well steel storm or mutilate can still be decent if you have excess mana and melee based since their effect is pretty strong.
but tbh its the first instance ever of trigger gems consuming mana in Siralim 
when i seen the message about trigger gems/listed mana cost id expect removing listed mana cost, not implementing but well.
since their use is random you can only rely on em in a group thats tottally independent on casting OR have their most important spells cost health. otherwise you wont be able to put that shell/multicast/whatever when you really need it
Actually those chance can be extremely relliable with melee builds. Idk its controversal. For now i ofc removed it from all the creatures because id rather rely on manual casting of whatever even weaker even if you 'd have 100% autocast of this on melee. not like you have spare 30 mana my nether has like 47 and it all goes to mana bomb heh